Method for manufacturing semiconductor device

ABSTRACT

A method for manufacturing a semiconductor device includes: preparing a Si substrate having a flat portion with flat front and back surfaces and a bevel portion located at a periphery of the flat portion; forming a III-V nitride semiconductor film on the front surface of the Si substrate by epitaxial growth; and after forming the III-V nitride semiconductor film, grinding the Si substrate from the back surface. Amounts of working at the bevel portion on the front surface and the back surface of an outermost end portion of the bevel portion are asymmetrical. A first thickness measured from the front surface of the flat portion to the outermost end portion is smaller than a second thickness measured from the back surface of the flat portion to the outermost end portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for manufacturing asemiconductor device wherein a III-V group nitride semiconductor film isepitaxial grown on a Si substrate.

2. Background Art

Epitaxial growth of a III-V group nitride semiconductor film,particularly Al_(x)Ga_(y)In_(z)N (x+y+z=1, y≠0) film as anelectronics/optoelectronics material has been proposed (see, forexample, Japanese Patent Laid-Open No. 2005-243727). As a method ofepitaxially growing this AlGaInN film, a metal organic chemical vapordeposition (MOCVD) is known.

Sapphire substrates have widely been used for epitaxial growth of GaN byMOCVD. However, sapphire substrates have a low degree of latticematching with GaN and have a thermal expansion coefficient differentfrom that of GaN, and attempts to improve the crystalinity of GaN wereunsuccessful in the past. In recent years, after the establishment of alow-temperature buffer layer technique, the crystalinity of GaN has beenimproved and the development of device manufacturing techniques mainlyfor blue and white LEDs has advanced remarkably.

However, it is difficult to further improve the crystalinity in terms ofdislocation reduction effect and so on. Sapphire itself has low heatconductivity, and heat cannot be sufficiently released from a deviceusing sapphire, resulting in a deterioration in performance of thedevice. Therefore, hopes are being consistently put on other substratematerials. SiC having a high degree of lattice matching and stable evenat a high temperature is one of candidates for use as a suitablesubstrate. With SiC, while its quality has been improved in recentyears, there are problems that its price is high and it is difficult toincrease the wafer diameter, as well as crystal quality problems such asmicropipes.

In contrast, an effect of increasing the wafer diameter and an effect ofreducing dislocations have been achieved for Si substrates, and Sisubstrates are steadily available at a low price. However, there is alattice matching problem and a thermal expansion coefficient differenceproblem with Si substrates and GaN. In a case where a low-temperatureAlN buffer layer and a GaN are successively grown on a sapphiresubstrate and the temperature of the substrate is thereafter returned toroom temperature, compressive stress acts in the GaN layer on thesapphire substrate, so that a crack is not easily caused in thesubstrate. In a case where these layers are formed on a Si substrate inthe same way, a tensile stress acts in the GaN layer and, therefore, acrack can easily be caused in the Si substrate. Further, there is, forexample, a melt-back etching problem relating to the reaction between Ga(or GaN) and Si. In spite of many problems including those describedabove, a practical level of use of Si substrates has been reached withthe advancement of techniques including multilayer buffer techniques inrecent years.

SUMMARY OF THE INVENTION

In manufacture of a semiconductor device, a III-V nitride semiconductorfilm is epitaxially grown by metal organic chemical vapor deposition,and the wafer is thinned by backgrinding. As backgrinding progresses,however, part of the III-V nitride semiconductor film on a bevel portion(the end surface and a peripheral sloped portion of the wafer) isexposed and comes off. Pieces of the III-V nitride semiconductor filmthat have come off are involved in grinding to locally grind the wafer.Chippings are thereby generated and the outer periphery of the wafer ischipped, resulting in a deterioration in productivity.

In view of the above-described problems, an object of the presentinvention is to provide a method for manufacturing a semiconductordevice which can improve the productivity.

According to the present invention, a method for manufacturing asemiconductor device includes: preparing a Si substrate having a flatportion with flat front and back surfaces and a bevel portion providedon a periphery of the flat portion; forming a III-V nitridesemiconductor film on the front surface of the Si substrate by epitaxialgrowth; and after forming the III-V nitride semiconductor film, grindingthe Si substrate from the back surface. Amounts of working for the bevelportion on the front surface side and the back surface side of anoutermost end portion of the bevel portion are asymmetrical. A thicknessfrom the front surface of the flat portion to the outermost end portionis smaller than a thickness from the back surface of the flat portion tothe outermost end portion.

The present invention makes it possible to improve the productivity.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are sectional views showing the method of manufacturing asemiconductor device according to the first embodiment of the presentinvention.

FIG. 3 is a sectional view showing a method of manufacturing asemiconductor device according to the comparative example.

FIGS. 4 to 9 are sectional views showing the method of manufacturing asemiconductor device according to the second embodiment of the presentinvention.

FIGS. 10 and 11 are sectional views showing the method of manufacturinga semiconductor device according to the third embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A method for manufacturing a semiconductor device according to theembodiments of the present invention will be described with reference tothe drawings. The same components will be denoted by the same symbols,and the repeated description thereof may be omitted.

First Embodiment

A method of manufacturing a semiconductor device according to a firstembodiment of the present invention will be described with reference tothe drawings. FIGS. 1 and 2 are sectional views showing the method ofmanufacturing a semiconductor device according to the first embodimentof the present invention.

First, as shown in FIG. 1, a Si substrate 1 having a flat portion withflat front and back surfaces and a bevel portion provided on theperiphery of the flat portion is prepared. The amounts of working forthe bevel portion on the front surface side and the back surface side ofthe outermost end portion of the bevel portion are asymmetrical. Thethickness from the front surface of the flat portion to the outermostend portion is smaller than the thickness from the back surface of theflat portion to the outermost end portion, and is, for example, 40 μm orless.

Next, as shown in FIG. 2, an Al_(x)Ga_(y)In_(z)N (x+y+z=1, y≠0) film 2,which is an example of a III-V nitride semiconductor film, isepitaxially grown on the front surface of the Si substrate 1 by MOCVD.In this growth, the deposition of the Al_(x)Ga_(y)In_(z)N film 2 isstopped at the outermost end portion and epitaxial growth does not takeplace in the region below the outermost end portion.

More specifically, the Si substrate 1 placed on a susceptor heated to apredetermined temperature by a heating device is held in a reactionfurnace. Trimethylaluminum, trimethylgallium, trimethylindium, or amixture gas consisting of two or more of these metal organic gases andammonia provided as a nitrogen raw material are introduced from a gasintroduction section into the reaction furnace together with a carriergas such as hydrogen or nitrogen, and the Al_(x)Ga_(y)In_(z)N film 2 isdeposited on the Si substrate 1 by the reaction between the metalorganic gases and ammonia. For example, in a case where a field effecttransistor (FET) is made on the Si substrate 1, an AlGaN buffer layerhaving a layer thickness of 1.5 μm, a GaN electron travel layer having alayer thickness of 1.0 μm and an Al_(0.2)Ga_(0.8)N electron supply layerhaving a layer thickness of 25 nm are successively deposited byepitaxial growth. Subsequently, electrodes and wiring are formed.

Next, the Si substrate 1 is grinded from the back surface. Grinding ofthe Si substrate 1, however, does not reach any point beyond theoutermost end portion in the thickness direction. For example, the Sisubstrate 1 is worked into a thin plate having a thickness of 40 μm.Finally, dicing, die bonding, wire bonding and packaging are performedto complete the semiconductor device.

The effects of the present embodiment will be described in comparisonwith a comparative example. FIG. 3 is a sectional view showing a methodof manufacturing a semiconductor device according to the comparativeexample. In the comparative example, the amounts of working for thebevel portion on the front surface side and the back surface side aresymmetrical. Therefore, as backgrinding progresses, part of theAl_(x)Ga_(y)In_(z)N film 2 on the bevel portion is exposed and comesoff. Pieces of the Al_(x)Ga_(y)In_(z)N film 2 that have come off areinvolved in grinding to locally grind the Si substrate 1. Chippings arethereby generated and the outer periphery of the Si substrate 1 ischipped, resulting in a deterioration in productivity.

In contrast, in the present embodiment, the amounts of working for thebevel portion on the front surface side and the back surface side areasymmetrical, and the thickness from the front surface of the flatportion to the outermost end portion is smaller than the thickness fromthe back surface of the flat portion to the outermost end portion.Therefore, even when backgrinding progresses, the Al_(x)Ga_(y)In_(z)Nfilm 2 is not easily exposed, thus suppressing the generation ofchippings and improving the productivity.

Second Embodiment

A method of manufacturing a semiconductor device according to a secondembodiment of the present invention will be described with reference tothe drawings. FIGS. 4 to 9 are sectional views showing the method ofmanufacturing a semiconductor device according to the second embodimentof the present invention.

First, as shown in FIG. 4, a Si substrate 1 having a flat portion withflat front and back surfaces and a bevel portion provided on theperiphery of the flat portion is prepared. The flat portion is thencovered with a mask 3.

Next, as shown in FIG. 5, an oxide film 4 is formed on the front surfaceside of the bevel portion of the Si substrate 1 by using thermal CVD.The thickness of the oxide film 4 is 2.5 μm. The mask 3 is thereafterremoved, as shown in FIG. 6.

Next, as shown in FIG. 7, Al_(x)Ga_(y)In_(z)N film 2 is epitaxiallygrown on the front surface of the Si substrate 1 by using MOCVD. Forexample, in a case where a field effect transistor is made on the Sisubstrate 1, the same making flow as that in the first embodiment isperformed. The oxide film 4 is thereafter removed, as shown in FIG. 8.Next, as shown in FIG. 9, the Si substrate 1 is grinded from the backsurface.

As described above, the oxide film 4 is formed on the font surface sideof the bevel portion to inhibit the epitaxial growth of theAl_(x)Ga_(y)In_(z)N film 2 on the front surface side of the bevelportion. Therefore, even when backgrinding progresses, theAl_(x)Ga_(y)In_(z)N film 2 is not easily exposed, thus suppressing thegeneration of chippings and improving the productivity.

It is desirable to set the thickness of the oxide film 4 equal to orlarger than the thickness of the Al_(x)Ga_(y)In_(z)N film 2 in order toprevent the epitaxial growth of the Al_(x)Ga_(y)In_(z)N film 2 on thefront surface side of the bevel portion. For example, when the thicknessof the Al_(x)Ga_(y)In_(z)N film 2 is 1.0 μm, the thickness of the oxidefilm 4 is also set to 1.0 μm.

Third Embodiment

A method of manufacturing a semiconductor device according to a thirdembodiment of the present invention will be described with reference tothe drawings. FIGS. 10 and 11 are sectional views showing the method ofmanufacturing a semiconductor device according to the third embodimentof the present invention.

First, as shown in FIG. 10, a Si substrate 1 having a flat portion withflat front and back surfaces and a bevel portion provided on theperiphery of the flat portion is prepared. The amounts of working forthe bevel portion on the front surface side and the back surface side ofthe outermost end portion of the bevel portion are asymmetrical. Thethickness from the front surface of the flat portion to the outermostend portion is smaller than the thickness from the back surface of theflat portion to the outermost end portion, and is, for example, 40 μm orless. Oxide film 4 is formed on the front surface side of the bevelportion by using thermal CVD, as in the case of the second embodiment.

Next, Al_(x)Ga_(y)In_(z)N film 2 is epitaxially grown on the frontsurface of the Si substrate 1 by using MOCVD, as in the case of thesecond embodiment. For example, in a case where a field effecttransistor is made on the Si substrate 1, the same making flow as thatin the first embodiment is performed. The oxide film 4 is thereafterremoved. Next, as shown in FIG. 11, the Si substrate 1 is grinded fromthe back surface.

In the present embodiment, the amounts of working for the bevel portionon the front surface side and the back surface side are asymmetrical, asin the case of the first embodiment, and the thickness from the frontsurface of the flat portion to the outermost end portion is smaller thanthe thickness from the back surface of the flat portion to the outermostend portion, as in the case of the first embodiment. Further, the oxidefilm 4 is formed on the font surface side of the bevel portion, as inthe case of the second embodiment, thereby inhibiting the epitaxialgrowth of the Al_(x)Ga_(y)In_(z)N film 2 on the front surface side ofthe bevel portion. Therefore, even when backgrinding progresses, theAl_(x)Ga_(y)In_(z)N film 2 is not easily exposed, thus suppressing thegeneration of chippings and improving the productivity.

It is desirable to set the thickness of the oxide film 4 equal to orlarger than the thickness of the Al_(x)Ga_(y)In_(z)N film 2 in order toprevent the epitaxial growth of the Al_(x)Ga_(y)In_(z)N film 2 on thefront surface side of the bevel portion. For example, when the thicknessof the Al_(x)Ga_(y)In_(z)N film 2 is 1.0 μm, the thickness of the oxidefilm 4 is also set to 1.0 μm.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

The entire disclosure of Japanese Patent Application No. 2013-145643,filed on Jul. 11, 2013 including specification, claims, drawings andsummary, on which the Convention priority of the present application isbased, is incorporated herein by reference in its entirety.

What is claimed is:
 1. A method for manufacturing a semiconductor devicecomprising: preparing a Si substrate including a flat portion havingmutually opposed flat front and flat back surfaces, wherein the flatfront and flat rear surfaces are separated by a thickness of the flatportion that is measured transverse to the flat front and flat rearsurfaces, and a bevel portion located at and extending outwardly from aperiphery of the flat portion, wherein the bevel portion includes anoutermost end portion that is located more distant from the flat portionthan any other part of the bevel portion, a first thickness of the flatportion is measured (i) from a first plane that is generally parallel tothe flat front surface and that intersects the outermost end portionclosest to the flat front surface, (ii) to the flat front surface, asecond thickness of the flat portion is measured (iii) from a secondplane that is generally parallel to the flat back surface and thatintersects the outermost end portion closest to the flat back surface,(iv) to the flat back surface, and the first thickness is smaller thanthe second thickness; epitaxially growing a III-V nitride semiconductorfilm on the flat front surface of the Si substrate; and afterepitaxially growing the III-V nitride semiconductor film, grinding andremoving part of the Si substrate from the flat back surface of the Sisubstrate.
 2. The method for manufacturing the semiconductor deviceaccording to claim 1, including stopping grinding and removing of partof the Si substrate from the flat back surface of the Si substratebefore reaching the first plane.
 3. The method for manufacturing thesemiconductor device according to claim 2, wherein the first thicknessis no more than 40 μm.
 4. The method for manufacturing the semiconductordevice according to claim 1, comprising: after preparing the Sisubstrate and before epitaxially growing the III-V nitride semiconductorfilm, forming an oxide film on a side of the bevel portion that iscloser to the flat front surface than to the flat back surface; andafter epitaxially growing the III-V nitride semiconductor film andbefore grinding and removing part of the Si substrate, removing theoxide film.
 5. The method for manufacturing the semiconductor deviceaccording to claim 4, including forming the oxide film to an oxide filmthickness and epitaxially growing the III-V nitride semiconductor filmto a semiconductor film thickness that is equal to or smaller than theoxide film thickness.
 6. The method for manufacturing the semiconductordevice according to claim 1, epitaxially growing Al_(x)Ga_(y)In_(z)N(x+y+z=1, y≠0) as the III-IV nitride semiconductor film.